Known in the art is a device for measuring vibrations including a microwave generator transmitting its energy through an antenna system to an object being investigated and the reflected microwave energy is sent through an antenna system to a detector, which also receives high-frequency reference oscillations (cf. K. K. Namitkov, V. F. Chepura "Measurement of Vibrations and Linear Displacements by means of Microwaves" in journal "Measuring Instruments" No. 5,1960).
In this device the antenna system is made in the form of a waveguide with a rectangular cross section. The flange of the waveguide is located close to the object to be investigated, as a rule, at a distance commensurable with the wavelength of the microwave generator. As this distance increases, the spatial resolution and sensitivity of such a device make worse.
Also known in the art is a device for measuring vibrations, includes a microwave generator whose energy is transmitted to the object being measured through an antenna system. The microwave energy is reflected from this object and through an antenna system comes to a detector, which is also supplied by reference high-frequency oscillations (cf. Stewart Ch., Proposed Massless Remote Vibration, Pickup, J. Acoust. Soc. Amer. v. 30, No. 7, 1958, pp. 644-645).
In this device the antenna system is made in the form of two separate horn antennas 50 mm in diameter and includes receiving and transmitting antennas.
This device is designed for operation at a distance of 250 mm from the vibrating surface. In this case the diameter of the monitored section on the object being investigated is equal to approximately 104 mm.
In this device the space resolution and sensitivity get worse as soon as the vibration pickup is removed from the vibrating surface for a distance of a few meters due to an increase in the diameter of the illuminated section of the object and reduction of the portion of the reflected energy taken by the receiving antenna. Thus, when the distance of the object to be studied is increased to 3 m, the diameter of the monitored section is equal to at least 700 mm, while the fraction of the reflected energy fed to the vibration pickup is reduced to at least a few orders of magnitude compared to the energy sent through a distance of 250 mm.
Furthermore, the adjustment of said antenna system of this device and its guidance to a definite section of a shaped object at considerable distances presents practical difficulties. Since the microwave radiation is invisible, the operator cannot evaluate the accuracy of adjustment of the antenna system.